When all the following solutes act as acids, the one with the weakest conjugate base is
a. H2SO3.
b. H2CO3.
c. HClO4.
d. HClO.
e. HF.
4. (Points: 1)
A sample of ammonia (Kb = 1.8 * 10^-5) is titrated with 0.1 M H2SO4. At the equivalence point, the pH is approximately
a. 1.
b. 5.
c. 7.
d. 9.
e. 11.
To determine the answer to the first question, we need to identify the solute with the weakest conjugate base among H2SO3, H2CO3, HClO4, HClO, and HF.
The strength of the conjugate base can be determined by looking at the acidity constant (Ka) or pKa of the corresponding acid. The weaker the acid, the stronger its conjugate base.
Let's compare the acids and their corresponding conjugate bases:
a. H2SO3 (Sulfurous acid) - Its conjugate base is HSO3-.
b. H2CO3 (Carbonic acid) - Its conjugate base is HCO3-.
c. HClO4 (Perchloric acid) - Its conjugate base is ClO4-.
d. HClO (Hypochlorous acid) - Its conjugate base is ClO-.
e. HF (Hydrofluoric acid) - Its conjugate base is F-.
From the given options, the solute with the weakest conjugate base will be the one with the strongest acid. Therefore, the answer is (c) HClO4 because HClO4 is a strong acid, making ClO4- the weakest conjugate base among the given options.
Now, let's move on to the second question.
To determine the pH at the equivalence point of a titration between a weak base (ammonia) and a strong acid (H2SO4), we need to consider the reaction between the base and acid.
The reaction between ammonia (NH3) and sulfuric acid (H2SO4) can be represented as:
NH3 + H2SO4 → (NH4)2SO4
At the equivalence point, the moles of the base (NH3) will be equal to the moles of the acid (H2SO4), resulting in the formation of (NH4)2SO4.
Since (NH4)2SO4 is a salt of a strong acid (H2SO4) and a weak base (NH3), it will hydrolyze in water, resulting in the formation of NH4+ and SO4 2- ions.
The hydrolysis reaction of (NH4)2SO4 is an acidic hydrolysis reaction, resulting in the formation of hydronium ions (H3O+). As a result, the solution will be acidic.
Therefore, at the equivalence point, the pH is expected to be less than 7. Among the options provided, the closest pH value to acidic conditions is (a) 1.
Hence, the answer to the second question is (a) 1.